Date of Award
Summer 6-26-2019
Degree Type
Thesis
Degree Name
Master of Science in Integrative Biology (MSIB)
Department
Biology
Committee Chair/First Advisor
Dr. Bill Ensign
Major Professor
Dr. Lisa Ganser
Second Committee Member
Dr. Martin Hudson
Abstract
Hyperekplexia is a neurological disorder affecting infants and can be characterized by excessive startle reactions in response to unexpected stimuli. This disease can be modeled in zebrafish in the bandoneon (beo) mutant, where the glrbbmutation results in glycine receptor (GLYR) loss of function glycine receptors and ultimately, improper inhibitory signaling. Though hyperekplexia is a glycinergic-based signaling disorder, disease symptoms are often alleviated with GABA-agonistic benzodiazepines. Exogenous cannabinoids also modulate GABAergic signaling, and THC, one of the natural compounds that prompted the discovery of the endocannabinoid system mimics the effects of endogenous cannabinoids at endocannabinoid and non-cannabinoid sites in the central nervous system. These cannabinoids also have therapeutic effects in animal models of seizures and epilepsy, leading to the aims of the present study to examine the developmental and behavioral influences of THC on wild-type (WT) and bandoneon (beo) embryos and to compare these effects to those observed after exposure to Lorazepam, a common benzodiazepine used to mitigate spasticity in hyperekplexics. Since both THC and Lorazepam restore balanced signaling, we hypothesized that THC would alleviate spasticity and Lorazepam would serve as a positive control inbeoembryos. We assessed embryonic growth parameters at 24, 48, 72, 96, and 120 hours post fertilization (hpf) following THC (0.2, 0.6, 2.0 and 5.0 mg/L) and Lorazepam (0.02 and 0.2 mg/L) exposure at 0-1hpf in WT and beoembryos. In WT and beoembryos, survival and hatching rates were inversely proportional to THC concentration confirming that THC exposure slows development and can impact survivorship. Morphological anomalies, however, increased with higher THC concentrations. We then assessed embryonic behavior using the innate escape response essential to survival at 24, 48, 72, 96, and 120 hpf following THC (0.2 and 2.0 mg/L) and Lorazepam (0.2 and 0.02 mg/L) exposure. Impacts on escape behavior varied, and when dosed with Lorazepam and THC, individuals displayed similar response times to controls at 24, 96, and 120 hpf. Significant differences in escape behavior times were measured at 48 and 72 hpf, specifically during the coil to relax phase of the escape response. During this time, beocontrol individuals were significantly different than 0.2 mg/L Lorazepam (p<0.0003 and p<0.0001 respectively) and 0.2 mg/L THC (p<0.0014 and p<0.0021 respectively). 0.2 mg/L THC was significantly different from 0.2 mg/L Lorazepam during the coil to relax phase of the escape response at 48 and 72 hpf (p<0.0014 and p<0.0002 respectively) and the total response time at 72 hpf (p<0.0201). These data suggest that THC exposure can deleteriously affect development and the establishment of neural circuits essential to survival, but can also alleviate spasticity symptoms depending on developmental stage and concentration.